I did recall a game involving Wolves which was probably the closest to a disaster, and knew it was in the 80's.... didn't realise it was as early as 81 though.

I go to a fair amount of football in Italy, where the grounds are way behind in terms of facilities and "quality" compared to the premier league (but absolutely streets ahead in terms of character and atmosphere).

Have never been fenced in over there, but even at Serie A grounds such as Bologna and Atalanta there are huge barriers at the front of the stand, and deep moats, to prevent pitch invasions. And one of my abiding memories of the massively high-profile showcase match AC Milan vs Juventus is the Curva Sud being massively overpopulated. Every time someone put a ticket through the automatic turnstiles, about three people without tickets also jumped through. If you go in an Ultra's end in Italy, forget about getting anywhere near your seat, it's just an absolute free-for-all....